Abstract

Olfactory ensheathing cells (ECs) are a promising tool for the repair of
injury in the adult central nervous system. However, important aspects of the cell
biology of ECs remain unclear, such as whether ECs exist as a single population or as
two subpopulations with Schwann cell-like and astrocyte-like characteristics. The morphologies
of these subpopulations are used as defining characteristics, yet ECs are
known to be morphologically plastic. To elucidate this apparent inconsistency, we
investigated the morphological plasticity of ECs in culture. We defined purified ECs as
immunopositive for both p75 neurotrophin receptor and glial fibrillary acidic protein. In
MEM D-valine modification 10% dialyzed fetal calf serum, 87%–90% of ECs displayed
a flat morphology. In three different serum-free media (N2 medium, neurobasal medium
B27 supplement, and DMEM/F-12 medium G5 supplement), 78%–84% of ECs
displayed process-bearing morphology. Ensheathing cells switched reversibly between
these morphologies within a day of the serum conditions being changed. Exposure to 1
nM endothelin-1 in serum-free medium prevented the switch from flat to processbearing
morphology, while 1 mM dibutyryl cAMP accelerated this change. The effects of
both agents were completely reversible and similar to that reported for astrocytes. Both
flat and process-bearing ECs were immunopositive for brain-derived neurotrophic factor,
nerve growth factor, neurotrophin-4, and TrkB but not TrkA. Together, these results
suggest that ECs exist as a single morphologically plastic population.